Apparatus for the treatment of a solid body

ABSTRACT

Plasma treatment apparatus includes means to generate a plasma jet at atmospheric pressure, and means to control both the cross-sectional size of the jet and the relative speed of movement between the jet and a body being treated.

FIELD OF THE INVENTION

This invention relates to the treatment of solid bodies and, morespecifically, it deals with an apparatus for the plasma treatment of thesurface of a solid body. The invention may be used, e.g. in electricalengineering, mechanical engineering, electronics and other fields.

BACKGROUND ART

Plasma technology for the treatment of solid bodies is now underintensive development to replace substantially liquid chemical kinds oftreatment in all operations. Various kinds of processing of the surfaceof solid bodies exist, including heat treatment, plasmochemical cleaningand etching, and film forming.

Known in the art are plants in which a plasma medium is provided under apressure of at least 10² Pa. Such vacuum plasma treatment plants includea vacuum chamber having a gas evacuation system and incorporating aplasma generator having a plasma forming gas supply system and a supportholder. A three-dimensional charge is excited in such vacuum plasmatreatment plants, and the support is stationary. For the excitation ofplasma, use is made of a high-frequency, SHF Super High Frequency, glow,or arc discharge which, according to the gas or cathode target materialused, forms a desired plasma composition for etching or film deposition.

Higher vacuum under these conditions contributes to a more uniformsurface treatment. However, a higher vacuum results in a decrease in thedensity of active particles and the lower flow of such particles towardsthe surface, so as to prolong the surface treatment period. This is oneof the reasons why the throughput capacity of such plants is inadequate.In addition, low throughput capacity is caused by the need for thecontinuous maintenance of the vacuum, i.e. evacuation of the wholeworking volume of the chamber. This is especially pronounced where theplasma forming gas is to be replaced, when it is necessary to carry outthe complete cleaning of particles from the chamber, so as to avoidhaving undesired impurities when starting a new cycle of surfacetreatment. This results in the need for a prolonged period ofpreparation of the plant for operation. When such plants are used forcontinuous manufacturing treatment processes, lock chambers are providedwhere there is a need for communication with atmosphere, so as toincrease the throughput capacity. In such arrangements, contamination ofthe supports can result, which is extremely undesirable, particularly inelectronic engineering.

SUMMARY OF THE INVENTION

These disadvantages are reduced in a plasma reactor described in U.S.Pat. No. 4,946,537 with a vacuum chamber which has a reagent gas supplysystem, a plasma generator, and at least one elctromagnetic coil whichis positioned coaxially with the chamber. A specimen is mounted in aholder inside the chamber to extend in parallel with a magnetic fieldgenerated by the coil. A high-energy flow of charged high-densityparticles from the plasma is incident perpendicularly upon the surfaceof the specimen so as to carry out the treatment.

High-energy ions interacting with the surface give rise toradiation-induced defects, i.e., to disruptions of structure andatomization of the material being treated and initiate radiation-inducedchemical reactions. As the degree of integration of chips grows higher,process layers in the active structures become thinner and thinner.Radition induced effects in such layers cause changes in electricalproperties and can even result in complete rejection of elements ofchips. Such a reactor cannot ensure the necessary high quality oftreatment.

It is an object of the invention to increase throughput capacity andenhance the quality of treatment of solid bodies.

In one embodiment of the invention to be described an apparatus forplasma treatment, preferably with planar supports, comprises a plasmagenerator having a plasma forming gas supply system and a power supply,and a support holder, the plasma generator including a generator of aplasma jet under atmospheric pressure having a regulator of thecross-sectional size of the plasma jet. The support holder and theplasma jet generator are mounted for movement with respect to each otherin the direction of at least one coordinate axis for regularlyintroducing the support holder into, and retracting it from thetreatment zone. The apparatus of this embodiment is also provided with ameans for setting the support holder speed and the cross-sectional sizeof the plasma jet, being connected to the regulator of thecross-sectional size of the plasma jet and with a drive for the supportholder. The drive for the support holder is capable of varying thesupport holder speed both within and outside the treatment zone.

One advantage of the apparatus to be described resides in its highthroughput capacity, the use in the apparatus of a plasma jet-generatorfor the atmospheric pressure jet allowing the processes of interactionof the plasma with the surface outside the vacuum chamber to beintensified. No vacuum equipment for evacuation and no sealed chamberare required so that the apparatus is always ready for operation. Unlikearrangements employing reduced-pressure plasma, the use of a plasmagenerator for an atmospheric pressure plasma jet enables the transfer ofactive particles (excited ions and atoms) towards the support surface tooccur through diffusion rather than through free molecular movement. Thedensity of the active particle flow in this case is very many timeshigher than that obtainable in vacuum plants. The active particlesdiffuse towards the surface under these conditions without any loss ofactivity as the flight distance for non-elastic interactions is muchgreater than the thickness of the boundary layer (the boundary layer isformed adjacent to the support surface when plasma jet flows around it,and its thickness is about 10-4 m (with q≈10⁷ W/m²). However, as aresult of elastic collisions in the boundary layer, the active particleslose their kinetic energy. Therefore, with a very high density of activeparticle flow, hence, with a high raze of photochemical processesoccurring on the surface, i.e., with a high speed of surface treatment,any radiation-induced damage is substantially excluded and a highquality of treatment can be achieved. As the thermal flux directedtowards the surface is high (plasma temperature is as high as ((10 to15).10³ K), this plasma can be used for treatment in an unsteady heatconductance mode, i.e., with a short term plasma action upon the surface(the residence time of a point under treatment in a plasma stream isabout 10 ms). This surface treament is a dynamic plasma operation (DPO).For carrying out this process, an apparatus must have systems forsetting up the jet size and the support speed and also devices forcarrying out a precision control of the relative movement of the plasmajet generator and the support.

For maintaining the desired size of the plasma jet during treatment, ameans for setting the cross-sectional size of the plasma jet includes abrightness detector in the particular embodiment. The brightnessdetector carries out monitoring and, following the receipt of an errorsignal, a command for correcting the size of the plasma jet is sent fromthe detector to the setting means.

In carrying out the treatment of a large number of identical parts, itis preferred that the support holder be in the form of a turret, so asto raise substantially the throughput capacity of the apparatus.

To provide for the possibility of the deposition of films of organometalcompounds and for carrying out etching, the plasma forming gas supplysystem has in certain embodiments to be provided with a vaporizer havinga thermo-controlled conduit for maintaining the organometal compounds inthe gaseous state. The free end of the thermo-controlled conduit isdirected towards the plasma jet zone. This increases the manufacturingcapabilities of the apparatus, owing to a broadening of the range oftypes of film that can be deposited.

To reduce the consumption of a plasma forming gas, the gas supply systemmay be provided with a controlled valve and the support holder may beprovided with a coordinate pickup, the signal of the pickup controllingthe valve so that the valve might be opened only at the moment thesupport passes through the treatment zone.

To increase the output of the process in treating parts having adiameter which is greater than the plasma jet size, the support may berotated about an axis drawn through its geometrical centreperpendicularly with respect to the support plane. This allows the wholesupport to be treated in a single pass.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of a specific embodiment thereof,especially when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective schematic illustration of one arrangement,

FIG. 2 is a diagrammatic and partly block schematic illustration of anapparatus having a brightness detector,

FIG. 3 is a block circuit diagram of a brightness detector,

FIG. 4 is a circuit diagram of means for setting the cross-sectionalsize of a plasma jet,

FIG. 5 is a circuit diagram of means for setting the speed of movementof a support,

FIG. 6 is a schematic illustration of a plasma forming gas supply systemhaving a controlled valve and a vaporizer, and

FIG. 7 is a perspective view of a support holder having an auxiliarydrive.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a most ingenuous embodiment of oneform of apparatus.

In this embodiment, a generator 1 for a plasma jet 2 is provided with aregulator of the cross-sectional size of the plasma jet 2, which may bein the form of an open-ended magnetic circuit 3 mounted coaxially withthe generator 1 and connected to a solenoid 4 which receives a controlsignal from a means 5 for setting the cross-sectional size of the plasmajet 2. The generator 1 is connected to a power supply 6, and a plasmaforming gas is supplied to the generator 1 from the system 7. A support8 is attached, e.g., by means of a vacuum suction device, to a holder 9which has a drive 10 controlled by a setting means 11 for setting-up thespeed of movement of the support 8. The holder 9 for the support 8performs a rotary motion. The generator 1 of the plasma jet 2 is mountedabove a plane defined by the path of movement of the holder 9, in such amanner that plasma jet intersects this path to define a supporttreatment zone. The setting means 5 may be in the form of a currentgenerator, e.g., a transistor having its base arranged to receive adrive signal in the form of a voltage from a variable resistor. The coilof the solenoid 4 is arranged in the emitter circuit of the transistor.

In the simplest case, the setting means 11 may be in the form of acontrolled pulse generator with a pulse rate determining the speed ofmovement of the holder 9 of the support 8. It is arranged that a changein the frequency of the controlled pulse generator corresponds to achange in speed of the support 8.

The operation of the apparatus will now be described with reference to aspecific example which involves the removal of a photo resistor maskfrom the surface of a silicon chip support.

Unlike previously proposed arrangements, the apparatus of thearrangement to be described allows the removal to be carried with aninert gas plasma, thereby ruling out undesired chemical effects upon thestructures formed as a result of a high-density flow of active particlestowards the surface being treated.

Direct current of 100 A is supplied to the generator 1 from the powersupply 6, and nitrogen as a plasma forming gas is supplied through thegas supply system 7. A signal from the setting means 5 determines thevalue of the current at the solenoid 4 to define the magnitude of themagnetic field induced by the magnetic circuit 3. The magnetic field ofthe open-ended magnetic circuit 2 causes the cross-sectional size of theplasma jet to be between 6 and 2 cm. These parameters ensure thenecessary power density of the plasma jet 2 for removing a photoresistive mask from the support 8. The setting means 11 sets up thespeed of movement of the support 8 in the treatment zone at 0.8 m/s.During the treatment, the support 8 is heated to 300° C. For thecomplete removal of the photo resistive mask from the support 8, thetreatment has to be repeated several times. The support 8 is preferablycooled down to a predetermined starting temperature before eachsuccessive treatment cycle. This step takes from 5 to 10 seconds. Theseconditions are taken into account in setting up the speed of movement ofthe support 8 outside the treatment zone.

It is preferable that, during successive treatment cycles, the plasmaparameters should remain unchanged, so that monitoring is required inorder to ensure that the conditions do not change. Monitoring of theconditions can be achieved by means of a brightness detector. The samereference numerals are used for similar parts of the apparatus in thedifferent figures of the drawings.

FIG. 2 shows an apparatus in which three brightness detectors 12 areprovided for monitoring the cross-sectional size of the plasma jet 2.The brightness detectors 12 are positioned in a plane drawn in parallelwith the plane of movement of the support 8. The brightness detectors 12keep a watch on the brightness distribution in the plasma jet 2continually, and error signals are fed from it to them setting means 5and 11 in order to allow the cross-sectional size of the plasma jet 2and the speed of movement of the support 8, respectively, to becontrolled. This control results in a high consistency in thereproducibility of the treatment results. This feature is especiallyimportant if a turret is used as a support holder 9 in order to increasesubstantially the throughput capacity of the apparatus in carrying out acontinuous treatment process using a large number of supports 8. In thiscase the generator 1 has a drive 13 controlled by the setting means 11.The drive 13 moves the generator 1 in the transverse direction withrespect to the path of movement of the support 8. This movement of thegenerator 1 allows a more uniform treatment of the support to be given,since the distribution of the energy density of the plasma jet 2 is notuniform and is at its maximum at the centre of the jet 2. The movementof the generator 1 corresponds to the movement of the plasma jet 2 alongthe surface of the support 8 being treated. For this reason, the centreof the plasma jet 2 will pass over the entire surface area of thesupport 8 during several consecutive treatment cycles.

The brightness detectors 12 used in the apparatus may be configured asshown in FIG. 3. A brightness detector 12 consists of a line 14 ofSCC-receivers, first and second analog switching circuits 15 and 16controlled by first and second counters 17 and 18, a comparator 19,first and second analog switches 20 and 21, an adder 22 an invertingadder 24, and an inverter 25.

This system is designed for monitoring the brightness and temperaturedistribution in the plasma jet 2 for evaluating changes in the plasmaparameters.

The system functions in the following manner.

Signals from the outputs of the receivers of the line 14 arrive at theinputs of the analog switching circuits 17 and 18, respectively. Thecounters 17 and 18 function in such a manner that signals from all ofthe receivers of the line 14 appear one-by-one at the output of theanalog switching circuit 15. Signals from the rest of the receivers ofthe line 14 appear one-by-one at the output of the switching circuit 16during the period within which a signal from the first receiver of theline 14 appears at the output of the switching circuit 15.

The outputs of the switching circuits 15 and 16 are connected to theinputs of the comparator 19, which has its output connected to controlthe inputs of the analog switches 20 and 21. A signal from the output ofswitching circuit 16 goes to the signal inputs of the analog switchingcircuits 20 and 21. The comparator 19 consecutively compares the signalfrom the first receiver of the line 14 with the signals from the rest ofthe receivers of the line 14. The comparison results arrive at thecontrol inputs of the analog switches 20 and 21, which are madeconductive once in order to let a signal through when there are nocontrol signals from the output of the comparator 19, the switch 20being made conductive when a maximum-value signal from the line 14 isdetected. The switch 21 is made conductive upon the detection of asecond-value signal from the line 14.

A signal, which is responsive to the maximum-value on the line 14, andwhich is obtained from the output of the switch 20 arrives at the addinginput of the adder 22 and at the control input of the counter 17, whichrecords the ordinal number of the receiver from the output of which thissignal has been sent. The receiver bearing this number will participateno more in the comparison procedure which is aimed at detecting themaximum value. After the detection of the maximum signal, a changeoccurs in the state of the counters 17 and 18, a signal from the secondreceiver of the line 14 appears at the output of the switching circuit15, and the procedure aimed at detecting the maximum value will berepeated. The detected signal, which will be the second one in value, isfed, via the switch 21, to the difference input of the adder 22. Thesignal from the output of the adder 22 is fed, via a multiplier 23, tothe input of the inverting adder 24, where it is added to a referencesignal U₁, and is fed, via the inverter 25, to the input of a brightnessdetector 12. There are three brightness detectors 12 connected to thesetting means 5, (FIG. 2) and signals U₂, U₃, and U₄ appear at theoutput of each of them respectively. These signals arrive at an input ofthe setting means 5 (FIG. 2). In this case, the setting means 5 is builtaround an adding inverter 26 (FIG. 4) having its output connected to thebase of a transistor 27. The transistor 27 converts the error signalobtained at the output of the adding inverter 26 into the current of itsemitter circuit in which the coil of the solenoid 4 is arranged. Acurrent proportional to the error signal of the setting means 5 willthus flow through the coil of the solenoid 4.

The setting means 11 receives signals from the brightness detectors 12at its input and functions in a similar manner. The setting means 11consists of an inverting adder 28 (FIG. 5) having its output connectedto a control input of a generator 29. The error signal from theinverting adder 28 is converted in this case at the output of generator29 into a varying pulse rate signal which controls the speed of movementof the drives 10 (FIG. 1) and 13 (FIG. 2).

The plasma forming gas supply system 7 in the apparatus of FIG. 2 doesnot allow coatings of organometal compounds to be deposited. To achievethis, the system 7 is provided with a vaporizer 30 (FIG. 6) having athermo-controller conduit 31 and a heater 32. The heater 32 maintains aconstant temperature in the conduit 31 in order to avoid condensation ofvapors of organometal compounds which are fed into the plasma jet 2 tobe desposited on support 8.

To reduce the consumption of gas and to combine operations such as thecleaning of support surfaces and the deposition of coatings, the system7 is provided with valves 33 and 34 mounted on the conduit of the system7 and on the conduit 31, respectively. Valves 33 and 34 arealternatively opened by a control signal received from a coordinatepickup 35, which is mounted, e.g., on the support holder 9. The pickup35 may be in the form of an aperture of a length corresponding to thesize of the surface of the support 8 being treated, a light sourceprovided on the one side of the aperture, and a photo sensitive elementprovided on the opposite side of the aperture. A signal from the outputof the photo sensitive element is a control signal for the valves 33 and34. The valves 33 and 34 are opened only for the time of the arrival ofthe signal, so as to reduce gas consumption. The valve 33 is opened inresponse to even signals and the valve 34 is opened in response to oddsignals, so as to ensure their consecutive operation. This operation ofthe apparatus allows its manufacturing capabilities to be enlarged andmakes it more cost-effective.

If the size of the support 8 is greater than the size of plasma jet 2,it is preferred that the support holder 9 be provided with an auxiliarydrive 36 (FIG. 7). The drive 36 rotates the support 8 about an axisdrawn perpendicularly with respect to its plane through the geometricalcentre of the support. This allows the treatment of the whole surface ofsupport 8 to be carried in a single pass thus greatly increasing thethroughput capacity of the apparatus.

The most preferred embodiments of the invention have been describedabove by way of example. It will be appreciated however that variationsand modifications can be made within the scope of the appended claims.Thus, the circuitry of such units as the movement speed setter, theplasma jet size setter, and the brightness detector may vary. The designof the support holder may also be modified.

We claim:
 1. Apparatus for use in the plasma treatment of a body,including a plasma jet generator, the plasma jet generator having meansfor generating a plasma jet at atmospheric pressure, a plasma forminggas supply system arranged to supply a plasma forming gas to thegenerator, and a support for a body to be treated with the plasma jet,being generated at atmospheric pressure, the plasma jet and the supportfor the body to be treated being mounted for successive relativemovements with respect to one another in one direction in at least onecoordinate axis in such a way that the support for the body and theplasma jet may be in or out of contact as required, means forcontrolling both the speed of relative movement between the support andthe plasma jet and the cross-sectional size of the plasma jet which isgenerated at atmospheric pressure according to the relative values ofthe said speed and the said size in order to provide a required degreeof treatment.
 2. Apparatus as claimed in claim 1 including means fordetecting the brightness of the plasma jet, the output of the means fordetecting the brightness of the plasma jet being used to control thecross-sectional size of the plasma jet.
 3. Apparatus as claimed in claim2 in which the output of the means for detecting the brightness of theplasma jet is used to control the speed of the relative movement betweenthe support and the plasma jet.
 4. Apparatus as claimed in claim 1wherein more than one support is included, and further including aturret for carrying more than one of said supports.
 5. An apparatus asclaimed in claim 1 in which the support for the body is rotatable aboutan axis drawn through the geometrical centre of the support and extendsperpendicularly with respect to a plane of the support.
 6. An apparatusas claimed in claim 1 wherein the plasma forming gas supply systemincludes a vapourizer, the vapourizer including a thermo-controlledconduit having a free end, the free end being directed towards theplasma jet so vapor flowing from the free end is incident on a portionof the plasma jet.
 7. An apparatus as claimed in claim 1 in which theplasma forming gas supply system has at least one passage including acontrolled valve, and a holder for the support has a coordinate pick upconnected to supply a signal to the controlled valve, whereby the supplyof the plasma forming gas may be controlled.
 8. The apparatus of claim 1further including means for controlling the cross-sectional area of theplasma Jet in response to an indication of the brightness of the plasmajet.
 9. Apparatus as claimed in claim 1 including means for detectingthe brightness of the plasma jet, and means responsive to the detectingmeans for controlling the cross-sectional area of the plasma jet. 10.Apparatus for use in the plasma treatment of a body, including a plasmajet generator, the plasma jet generator having means for generating aplasma jet at atmospheric pressure, a plasma forming gas supply systemarranged to supply a plasma forming gas to the generator, and a supportfor a body to be treated with the plasma jet, the plasma jet beinggenerated at atmospheric pressure, the plasma jet and the support forthe body to be treated being mounted for relative movement with respectto one another in the direction of at least one coordinate axis in sucha way that the support for the body and the plasma jet may be in or outof contact as required, means for controlling (1) the speed of relativemovement between the support and the jet both in and out of contact withone another and (2) the cross-sectional size of the plasma jet which isgenerated at atmospheric pressure, the controlling means including meansfor detecting the brightness of the plasma jet, the output of the meansfor detecting the brightness of the plasma jet being used to control thecross-sectional size of the plasma jet.
 11. Apparatus as claimed inclaim 10 in which the output of the means for detecting the brightnessof the plasma jet is used to control the speed of the relative movementbetween the support and the plasma jet.
 12. Apparatus for use in theplasma treatment of a body comprising a plasma jet generator, a supportfor a body to be treated with the plasma jet, the plasma jet and thesupport for the body to be treated being mounted for relative movementwith respect to one another in the direction of at least one coordinateaxis in such a way that the support for the body and the plasma jet maybe in or out of contact as required, means for controlling (1) the speedof relative movement between the support and the jet both in and out ofcontact with one another and (2) the cross-sectional size of the plasmajet, the controlling means controlling the cross-sectional area of theplasma jet in response to an indication of the plasma jet brightness.13. The apparatus of claim 12 wherein the controlling means controls therelative speed of the support of the plasma jet.
 14. The apparatus ofclaim 13 further including means for detecting the plasma jetbrightness, the controlling means for the cross-sectional area and therelative speed being responsive to the detecting means.
 15. Theapparatus of claim 12 further including means for detecting the plasmajet brightness, the controlling means for the relative speed beingresponsive to the detecting means.